The federal health care overhaul makes some notable improvements in insurance coverage for young adults.

They can now stay on their parents' health plans until they turn 26. Next year they can also look for subsidized coverage on the state-based insurance marketplaces, also called exchanges. And they may qualify for Medicaid, if their income are less than 138 percent of the federal poverty level ($15,856 in 2013).

So far, so good.

But young women who get pregnant may encounter unexpected gaps in coverage. Although the law requires most individual and small group plans to provide maternity and newborn care, large group plans aren't subject to those rules.

Now, that's not a problem for most women because the Pregnancy Discrimination Act of 1978 requires that companies with 15 or more workers that provide health insurance include maternity coverage for employees and their spouses. (Maternity coverage generally refers to prenatal care, labor and delivery, and some postpartum care.)

However, the law doesn't require maternity coverage for dependent children and, according to Dan Priga, who heads the performance audit group at human resources consultant Mercer, roughly 70 percent of large self-funded employers that pay their workers' claims directly don't provide it.

It gets weirder. Under the law, large and small employers alike are required to provide a range of preventive services without any out-of-pocket cost to patients. Among these are preconception and prenatal care, which typically includes tests and screenings to manage risks and help ensure a healthy pregnancy and birth.

The only plans that are excluded are those with grandfathered status under the law.

So a young pregnant woman who's insured as a dependent on her parents' large-group plan might find herself with insurance coverage for office visits and care leading up to childbirth, but no coverage for the actual labor and delivery, where the majority of costs are incurred.

It's too soon to say the extent to which this could be a problem, but patient advocates aren't dismissing it.

"It's certainly possible that employers would choose to cover only the bare minimum," says Adam Sonfield, a policy specialist at the Guttmacher Institute, a reproductive health research and policy organization.

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